Four Baltimore police officers have been suspended as part of an investigation stemming from the conviction of an officer for conspiring with a drug informant to orchestrate arrests, according to sources with knowledge of the case.

Anthony Guglielmi, the agency's chief spokesman, confirmed that the four officers were suspended from the Northwest District, where Richburg had worked in a special plainclothes unit. He declined to identify the officers or say why they were suspended.

"This is part of the commissioner's plan to root out corruption and get ahead of inappropriate, unethical behavior," Guglielmi said. "These officers were identified as part of an internal investigation and suspended."

Sources said the suspensions were part of the fallout after Detective Kendell Richburg pleaded guilty in federal court last month to an armed drug conspiracy charge. Police and prosecutors said he conspired with a drug informant to support the informant's drug dealing and raise the number of arrests he made.

Richburg, 36, faces a minimum sentence of 10 years and a maximum of life in prison at his sentencing in June.

U.S. Attorney Rod J. Rosenstein told The Baltimore Sun last week that the Richburg case was continuing.

"There is an ongoing federal criminal investigation as a result of evidence gathered during the wiretap investigation. I cannot comment about who may or may not be a suspect," Rosenstein said in an email.

Richburg's attorney, Warren Brown, said after his client's guilty plea that pressure to make arrests permeates the department and led to his client's criminal conduct.

"I listened to hundreds of hours of wiretapped conversations in the case," said Brown. "And I can tell you that if the curtain was pulled back, you would see that his M.O. was standard operating procedure. That's the way a lot of them work, because they're being judged by those numbers."

Police dismissed that allegation and said Richburg had only himself to blame for his conduct.

Rosenstein said federal prosecutors have met with city prosecutors about a handful of cases connected to the Richburg investigation in which they believe false police reports led to criminal charges. City prosecutors are reviewing the cases to determine whether they should proceed.

The Sun reported last month on the case of Brenda Brown, a 52-year-old who said she was arrested after buying three small bags of marijuana at a bus stop in September 2012.

In Richburg's plea, he said that he had instructed his informant to sell drugs to Brown so that he could arrest her, and he wrote in charging documents that he witnessed the sale even though he did not. Brown pleaded guilty and received a sentence including a year of probation, court costs, counseling and drug testing.

The Northwest District has been under fire in recent years, with the convictions of Officer Daniel Redd, who dealt drugs while on the job, and Richburg. Richburg worked in the Violent Crimes Impact Section, a unit lauded by police commanders for its work in high-crime areas but which has seen several officers accused of misconduct in recent years.

Police Commissioner Anthony W. Batts reduced the number of officers in the unit, renamed it the Zone Enforcement Section, and put it under the control of the patrol division.

Grayling Williams, the Police Department's internal affairs chief, said his office investigated the Richburg case in conjunction with the FBI. Last week, Williams informed the department that he was leaving to take a job with the Pennsylvania attorney general's office.

He declined to comment on the recent suspensions and developments in the case. But in an interview about his 16 months in Baltimore, he said the agency is working hard to investigate misconduct. Despite spending his time focused on bad cops, he said, he leaves with a good impression of the department.

"This department is serious about dealing with misconduct and integrity issues," Williams said. "It's just a matter of dealing with the few bad apples that are in this department. But the department itself really should not be painted as a department full of bad apples."